Cryogenics

Summary

Cryogenics is the branch of physics concerned with creating extremely low temperatures and the natural phenomena that result from subjecting various substances to those temperatures. At temperatures near absolute zero, the electric, magnetic, and thermal properties of most substances are greatly altered, allowing practical industrial, automotive, engineering, and medical applications.

Definition and Basic Principles

Cryogenics comes from two Greek words: kryo, meaning "frost," and genic, "to produce." This science studies the implications of producing extremely cold temperatures and how those temperatures affect substances such as gases and metals. Cryogenic temperature levels are not found naturally on Earth.

The usefulness of cryogenics is based on scientific principles. The three basic states of matter are gas, liquid, and solid. Matter moves from one state to another by the addition or subtraction of heat (energy). The molecules or atoms in matter move or vibrate at different rates depending on the level of heat. Extremely low temperatures, such as those achieved through cryogenics, slow the vibration of atoms and can change the state of matter. For example, cryogenic temperatures are used in the liquefaction of atmospheric gases such as oxygen, nitrogen, hydrogen, and methane for diverse industrial, engineering, automotive, and medical applications.

Sometimes cryogenics and cryonics are mistakenly linked, but the use of subzero temperatures is the only thing these practices share. Cryonics is the practice of freezing a body right after death to preserve it for a future time when a cure for a fatal illness or remedy for fatal injury may be available. The practice of cryonics is based on the belief that technology from cryobiology can be applied to cryonics. Adherents believe that if cells, tissues, and organs can be preserved by cryogenic temperatures, then perhaps whole bodies can be preserved for future thawing and life restoration.

Background and History

The history of cryogenics follows the evolution of low-temperature techniques and technology. Principles of cryogenics can be traced back to 2500 Before the Common Era (BCE), when Egyptians evaporated water through porous earthen containers to produce cooling. The ancient Chinese, Romans, and Greeks collected ice and snow from the mountains and stored it in cellars to preserve food. In the early 1800s, American inventor Jacob Perkins created a sulfuric-ether ice machine, a precursor to the refrigerator. In the mid-1800s, William Thomson, a British physicist better known as Lord Kelvin, theorized that extremely cold temperatures could stop the motion of atoms and molecules. This theoretical temperature became known as absolute zero, and the Kelvin scale of temperature measurement emerged.

Scientists of the time focused on the liquefaction of permanent gases. By 1845, British physicist Michael Faraday had achieved liquefaction of permanent gases by cooling immersion baths of ether and dry ice followed by pressurization. Six permanent gases—oxygen, hydrogen, nitrogen, methane, nitric oxide, and carbon monoxide—still resisted liquefaction. In 1877, French physicist Louis-Paul Cailletet and Swiss physicist Raoul Pictet produced drops of liquid oxygen, working separately and using completely different methods. In 1883, S. F. von Wroblewski at the University of Krakow discovered that oxygen would liquefy at 90 kelvins (K) and nitrogen at 77 K. In 1898, Scottish chemist and physicist James Dewar discovered the boiling point of hydrogen to be 20 K and its freezing point to be 14 K.

Helium has the lowest boiling point of all known substances. It was liquefied in 1908 by Dutch physicist Heike Kamerlingh Onnes at the University of Leiden, who was also the first person to use the word "cryogenics." In 1892, Dewar invented the Dewar flask, a vacuum flask designed to maintain temperatures necessary for liquefying gases—the precursor to the thermos. The liquefaction of gases had many critical commercial applications, and many industries use Dewar's concept in applying cryogenics to their processes and products.

The usefulness of cryogenics continued to evolve, and by 1934, the concept was well established. During World War II, scientists discovered that metals became resistant to wear when frozen. In the 1950s, the Dewar flask was improved with the multilayer insulation (MLI) technique for insulating cryogenic propellants used in rockets. Over the next thirty years, Dewar's concept led to the development of small cryocoolers, useful to the military in national defense. The National Aeronautics and Space Administration (NASA) space program applies cryogenics to its programs. Cryogenics can be used to preserve food for long periods—this is especially helpful during natural disasters. Cryogenics continues to grow globally and serve a wide variety of industries.

How It Works

Cryogenics is an ever-expanding science. The basic principle of cryogenics is that the creation of extremely low temperatures will affect the properties of matter, so the changed matter can be used for a number of applications. Four techniques can create the conditions necessary for cryogenics: heat conduction, evaporative cooling, rapid-expansion cooling (Joule-Thomson effect), and adiabatic demagnetization.

Creating Low Temperatures. With heat conduction, heat flows from matter of higher temperature to matter of lower temperature in what amounts to a transfer of thermal energy. As the process is repeated, the matter cools. This principle is used in cryogenics by allowing substances to be immersed in liquids with cryogenic temperatures or in an environment such as a cryogenic refrigerator for cooling.

Evaporative cooling is demonstrated in the human body when heat is lost through liquid (perspiration) to cool the body via the skin. Perspiration absorbs heat from the body, which evaporates after it is expelled. In the early 1920s in Arizona, during the summers, people hung wet sheets inside screened sleeping porches. Electric fans pulled air through the sheets to cool the sleeping space. In the same way, a container of liquid can evaporate so that the heat is removed as a gas; repeating the process drops the temperature of the liquid. An example is reducing the temperature of liquid nitrogen to its freezing point.

The Joule-Thomson effect occurs without the transfer of heat. Temperature is affected by the relationship between volume, mass, pressure, and temperature. The rapid expansion of a gas from high pressure to low pressure results in a temperature drop. This principle was employed by Onnes to liquefy helium, and it is useful in-home refrigerators and air conditioners.

Adiabatic demagnetization uses paramagnetic salts to absorb energy from liquid, resulting in a temperature drop. The principle of adiabatic demagnetization is the removal of the isothermal magnetized field from matter to lower the temperature. This principle is useful in application to refrigeration systems, which may include a superconducting magnet.

Cryogenic Refrigeration. Cryogenic refrigeration, used by the military, laboratories, and commercial businesses, employs gases such as helium (valued for its low boiling point), nitrogen, and hydrogen to cool equipment and related components to temperatures lower than 150 K. The selected gas is cooled through pressurization to liquid or solid forms (dry ice used in the food industry is solidified carbon dioxide). The cold liquid may be stored in insulated containers until used in a cold station to cool equipment in an immersion bath or with a sprayer.

Cryogenic Processing and Tempering. Cryogenic processing or treatment increases the length of wear of many metals and some plastics using a deep-freezing process. Metal objects are introduced to cooled liquid gases, such as liquid nitrogen. The computer-controlled process takes about seventy-two hours to affect the molecular structure of the metal. The next step is cryogenic or heat tempering to improve the strength and durability of the metal object.

Applications and Products

Early applications of cryogenics targeted the need to liquefy gases. The success of this process in the late 1800s paved the way for more study and research to apply cryogenics to developing life needs and products. Examples include applications in the automobile and healthcare industries, the development of rocket fuels, and food preservation. Cryogenic engineering has applications related to commercial, industrial, aerospace, medical, domestic, and defense ventures.

Superconductivity Applications. One property of cryogenics is superconductivity. This occurs when the temperature is dropped so low that the electrical current experiences no resistance. Superconductivity is important in magnetic resonance imaging (MRI), which uses a powerful magnetic field generated by superconducting electromagnets to diagnose certain medical conditions. The superconducting coils are cooled by liquid helium, which becomes a free-flowing superfluid, and liquid nitrogen cools the superconducting compounds, making cryogenics an integral part of this process. Another application is using liquefied gases to spray on buried electrical cables to minimize wasted power and energy and to maintain cool cables with decreased electrical resistance.

Health Care Applications. The healthcare industry recognizes the value of cryogenics. Medical applications using cryogenics include the preservation of cells or tissues, blood products, semen, corneas, embryos, vaccines, and skin for grafting. Cryotubes with liquid nitrogen are useful in storing strains of bacteria at low temperatures. Chemical reactions needed to release active ingredients in statin drugs used for cholesterol control must be completed at very low temperatures (–100 degrees Celsius). High-resolution imaging, like MRI, depends on cryogenic principles for the diagnosis of diseases and medical conditions. Dermatologists use cryotherapy to treat warts or skin lesions.

Food and Beverage Applications. The food industry uses cryogenic gases to preserve and transport mass amounts of food without spoilage. This is particularly useful when supplying food to war zones or natural disaster areas. Deep-frozen food retains its color, taste, and nutrient content while its shelf life is significantly increased. Certain fruits and vegetables can be deep frozen for consumption out of season. Freeze-dried foods and beverages, such as coffee, soups, and military rations, can be safely stored for long periods without spoilage. Restaurants and bars use liquid gases to store beverages while maintaining the taste and look of the drink.

Automotive Applications. The automotive industry employs cryogenics in diverse ways. One technique makes use of the property of thermal contraction. Because materials will contract when cooled, the valve seals of automobiles are treated with liquid nitrogen, which causes them to shrink to allow insertion and then expand as they warm up, resulting in a tight fit. The automotive industry also uses cryogenics to increase strength and minimize wear of metal engine parts, pistons, cranks, rods, spark plugs, gears, axles, brake rotors and pads, valves, rings, rockers, and clutches. Cryogenic-treated spark plugs can increase an automobile's horsepower and gasoline mileage. Using cryogenics allows a race car to race as many as thirty times without a major rebuild on the motor, in contrast to an untreated car, which could only race twice.

Aerospace Industry Applications. NASA's space program uses cryogenic liquids to propel rockets. Rockets carry liquid hydrogen for fuel and liquid oxygen for combustion. Cryogenic hydrogen fuel is what enabled NASA's space shuttles to get into orbit. In addition, liquid helium is used to cool the infrared telescopes on rockets.

Tools, Equipment, and Instrument Applications. Metal tools can be cryogenically treated to increase their wear resistance. Surgery or dentistry tools can be expensive, and cryogenic treatment can prolong their usage. Sports equipment, such as golf clubs, also benefit from cryogenics, providing increased wear resistance and better performance. Scuba divers acan stay submerged for hours using an insulated Dewar flask of cryogenically cooled nitrogen and oxygen. Some people claim musical instruments receive benefits from cryogenic treatment; in brass instruments, a crisper and cleaner sound is allegedly produced with cryogenic enhancement.

Other Applications. Other applications are evolving as industries recognize the benefits of cryogenics to their products and programs. The military has used cryogenics in various ways, including infrared tracking systems, unmanned vehicles, and missile-warning receivers. Companies can immerse discarded recyclables in liquid nitrogen to make them brittle, making them easier to pulverize or grind down to a more environmentally friendly form.

Careers and Course Work

Careers in cryogenics are as diverse as the applications of cryogenics. Interested persons can enter the profession in various ways, depending on their field of interest. Some secure jobs through additional education, while others learn on the job. Common jobs in the field of cryogenics include engineers, technologists or technicians, and researchers.

A primary career track for those interested in working in cryogenics is cryogenic engineering. To become a cryogenic engineer requires a bachelor's or master's degree in engineering. Coursework may include thermodynamics, production of low temperatures, refrigeration, liquefaction, solid and fluid properties, and cryogenic systems and safety.

Social Context and Future Prospects

The economic and ecological impact of cryogenic research and applications holds global promise for the future. In 2009, Dutch company Stirling Cryogenics built a liquid-argon cooling system for the ICARUS experiment, a neutrino study being carried out by Italy's Istituto Nazionale di Fisica Nucleare (National Institute of Nuclear Physics); the system, which maintains four hundred liters of liquid argon at a temperature of 94 kelvins, was designed to run nonstop for ten years. The Cryogenic and Refrigeration Engineering Research Centre (CRERC) at China's Technical Institute of Physics and Chemistry was created to explore new innovations and technology in cryogenic engineering. Both government agencies and private industries in the United States are pursuing innovative ways to use existing applications and define future implications of cryogenics. For example, a company in Cornwall, England, developed cryogenic technology to generate clean energy from methane, which is released in great quantities by cows. Other companies are using cryogenics to develop new ways to use liquid nitrogen in vehicles that transport goods at different temperatures.

As the twenty-first century progressed, innovation in cryogenics continued. Cryogenics was being explored for use in cryopreservation, a new technology that scientists were hopeful could extend the life of stem cells, organs, and tissue for transplant and reproductive cells used in fertility treatment. Additional uses of cryogenics were also being explored in the medical and biomedical fields and the heating and cooling industries. Although cryogenics has proved helpful to many industries, its full potential as a science has yet to be realized. Although cryogenics has proved useful to many industries, its full potential as a science has not yet been realized.

Bibliography

Extance, Andy. "Cool Innovations for Clean Energy." Physics World, 14 Nov. 2018, physicsworld.com/a/cool-innovations-for-clean-energy. Accessed 28 May 2024.

Hayes, Allyson E., ed. Cryogenics: Theory, Processes and Applications. Hauppauge: Nova, 2010.

Incer-Valverde, Jimena, et al. "Improvement Perspectives of Cryogenics-Based Energy Storage." Renewable Energy, vol. 169, May 2021, pp. 629–40, DOI:10.1016/j.renene.2021.01.032. Accessed 1 Mar. 2022.

“Innovations in Cryogenic Freezing: Applications and Technologies.” Cryometrix, 15 Apr. 2024, cryometrix.com/2024/04/15/innovations-in-cryogenic-freezing-applications-and-technologies. Accessed 28 May 2024.

Jha, A. R. Cryogenic Technology and Applications. Burlington: Elsevier, 2006.

Maytal, Ben-Zion, and John M. Pfotenhauer. Miniature Joule-Thomson Cryocooling: Principles and Practice. New York: Springer, 2013.

Pavese, Franco, and Gianfranco Molinar Min Beciet. Modern Gas-Based Temperature and Pressure Measurements. 2nd ed. New York: Springer, 2013.

Van Sciver, Steven W. Helium Cryogenics. 2nd ed. New York: Springer, 2012.

Ventura, Guglielmo, and Lara Risegari. The Art of Cryogenics: Low-Temperature Experimental Techniques. Burlington: Elsevier, 2008.

Zhavoronkav, Alex. “The Spring Of Cryobiology: One Enabling Technology That Will Help Build The New Industry Of The Future.” Forbes, 22 Sept. 2022, www.forbes.com/sites/alexzhavoronkov/2022/09/22/the-spring-of-cryobiology-one-enabling-technology-that-will-help-build-the-new-industry-of-the-future/?sh=669cdfee7699. Accessed 28 May 2024.